1. Field of the Invention
The present invention relates generally to systems for manufacturing high quality cast products and, more particularly, to accurately fabricating a fully dense composite injection molding tool element intended for repeated use.
2. Description of the Prior Art
Known vacuum casting systems have been used to prototype parts up to about six feet in length, including car bumpers and aircraft turbine blades. The key component of each system comprises a vacuum chamber with two sections. The upper section serves to mix the resin and the lower section is for casting the resin into the mold. First, an inexpensive mold is produced by casting over a master model in silicone rubber. The master model can be made in wax, wood, plastic, metal, or stereolithography materials. After curing, the mold is placed in the lower chamber of the machine. Resin is mixed in the upper chamber and gravity-fed through a plastic hose into the mold below it. The mixing and casting procedures take place in a vacuum of about 28 inches Hg. This eliminates bubbles and voids in both the mold and the plastic prototype part.
Many specially-formulated resins for vacuum casting are available to provide various characteristics in hardness, toughness, flexibility, and temperature resistance. The casting and curing steps can be completed in about 20 to 90 minutes. All resins can be colored through use of pigments.
The final vacuum cast product is a precise replica of the master, dimensionally accurate without blemishes, with all profiles and textures faithfully reproduced. This system is capable of achieving finishes equivalent to those obtained by injection molding with ABS.
Typical of the prior art relating to injection molding is U.S. Pat. No. 5,639,416 issued Jun. 17, 1997 to Pennisi et al. which discloses a process for molding dimensionally stable accurate plastic articles using a low pressure injection molding technique with a two-piece silicone rubber mold having a cavity representative of the shape of the article to be molded.
U.S. Pat. No. 4,927,600 issued May 22, 1990 to Miyashita et al. discloses a method for molding powders of metals or ceramics comprising allowing a pouch-like member of thin-walled rubber-like resilient material to be expanded into tight contact with the inner surface of an air-permeable mold carrier of a powdered filler material maintained under a negative pressure for holding its form, thereby producing a mold, charging starting powders into the mold, discharging air from the inside of the mold through an opening of the pouch-like member, then sealing the mold, then disintegrating the air-permeable mold carrier for removing a pre-molded body or article enclosed in the pouch-like member, and processing the pre-molded body by a cold or hot isostatic press for increasing the density of the pre-molded body or article.
The following patents disclose various operations including mixing, potting, curing, molding, and impregnating all while being performed in a vacuum:
______________________________________ U.S. Pat. No. Inventor(s) Issued ______________________________________ 4,657,714 Kenmochi et al. 04-14-87 4,655,700 Ahmed 04-07-87 4,412,804 Huther 11-01-83 4,374,081 Hiltz et al. 02-15-83 3,081,492 Grzegorczyk 03-19-63 2,696,022 Steinboek et al. 12-07-54. ______________________________________
The following U.S. patents all disclose evacuation of molding apparatus in order to remove dissolved gasses from the polymer-based mixture employed in the molding process:
______________________________________ U.S. Pat. No. Inventor(s) Issued ______________________________________ 5,518,385 Graff 05-21-96 5,435,943 Adams et al. 07-25-95 5,340,512 Slocum et al. 08-23-94 5,248,467 Cushman 09-28-93 5,059,112 Wieser 10-22-91 4,997,606 Mears et al. 03-05-91 4,439,386 Antczak 03-27-84 3,975,479 McClean 08-17-76. ______________________________________
It was with knowledge of the foregoing state of the technology that the present invention has been conceived and is now reduced to practice.